Although nursing homes (NH) are health care facilities, the scant existing literature identifies physicians as a shadowy presence in most NHs. Such limited involvement precludes full integration of physicians into the culture of the NH and potentially impedes interdisciplinary communication and effective treatment. Residents consequently suffer undesirable outcomes (e.g., avoidable hospitalizations, inappropriate medications, inadequate decubiti and wound care). Evidence to date suggests that the presence of nurse practitioners and physician assistants (NP/PAs), as well as involved physicians (referred to as medical staff) improves care, but there is substantial inter- and intra-state variation in the availability of these resources. This project examines the impact of state policies, and nursing-home and physician market factors on medical staff organization (MSO) and consequently on patient outcomes. There are four overall goals of this project: 1) to describe the medical steff organization in nursing homes, 2) to examine the effect of MSO and nursing home care processes, 3) to examine the effect of MSO on resident outcomes, and 4) to test the impact of state policies and local market resource factors on MSO. The project will use primary data collected in the P01 core surveys of nursing home administrators and directors of nursing that will identify aspects of MSO with a focus on control as demonstrated by contractual arrangements, credentialing, admitting privileges and other operating guidelines governing medical staff availability andresponsibilities, as well as nurse perceptions of unmet needs for medical staff support. Three years of secondary data (2000, 2004, 2008) from physician billing (Medicare Part B claims) for nursing home residents, physician credentials (UPIN Group File and American Medical Association Masterfile), nursing home information (from the Online Survey Certification Automated Records), data on state policies (collected at Brown University) and market resources from the Area Resource File and the Dartmouth Atlas will provide a wealth of data, and will be analyzed using difference in difference methods that allow for causal inference. Because so little is known about how physicians practice in NHs, this knowledge will be useful to facilities striving to improve quality of care, to regulators wishing to improve quality assurance, and to policymakers addressing NH reimbursement and regulation. Results will be disseminated broadly. Lay Summary: Physicians who treat NH patients often have limited involvement in the nursing home. Little is known about the effect of these physicians' practices on quality of care. This study will identify the impact of state policies and market factors on how medical services are organized in nursing homes and how these practices affect NH residents' outcomes.